Wakeman—Pigments of Flowering Plants. 803 
in the twigs, bark, leaves and shell of the unripe fruit, but not 
in the shells of ripe nuts, a and ^-hydrojuglones, trihydroxy 
naphthalenes, are also found. These colorless hydrojuglones, 
during the ripening of the nuts, are undoubtedly oxidized to 
the yellowish red juglone. Indeed the oxidation may well be 
carried farther, for juglone is readily oxidized by exposure to 
the air into hydroxy juglones which are still darker in color. 
There is no record, however, of the hydroxy juglones having 
been isolated from the walnut material. Juglone is also found 
in the green shells of the nuts and the bark of the twigs of Jug- 
lans nigra , the black walnut, Juglans cinerea , 2 ) the butternut; 
in the leaves of Cary a olivaef&i'mis, 2 ) the pecan; and in the bark 
of the twigs of Pterocarya caucasia 2 ) 
The possibilities for combination between juglone and the 
hydrojuglones must not be overlooked in considering the dark 
colored pigments in the walnut shells. Not only is there the 
possibility of juglone combining with each « and /3-hydrojuglone 
to form the corresponding quinhydrones; but the additional 
possibilities of its forming phenoquinones with itself, through 
the addition of its phenol group to a carbonyl group, and also 
of forming phenoquinones with the hydro juglones. If jug¬ 
lone be oxidized in the plant to hydroxy juglones the possibil¬ 
ities for pheno quinone and quinhydrone formation become 
fully as great as with the thymoquinones in the Monarda species. 
Pigments referable to a Methyl dihydro naphthalene 
Cio H 9 ch 3 
Methyldihydro-Naphthalene 
C 10 H 3 0 2 (OH), CH, 
Dihydroxy-methyl 
Naphthaquinone 
C 10 H fi 0 2 CH 3 
Methyldihydro-Naphthaquinone 
C 10 H 2 (OH) 3 0 2 ch 3 
Trihydroxy-methyl 
N aphthaquinone 
Two pigments, one orange red, crystallizing in needles, and 
the other red, crystallizing in plates, have been isolated from 
the root tubers of Prosera Whittakeri. The former is apparently 
dihydroxy methyl naphthaquinone and the latter trihydroxy 
methyl naphthaquinone. 
Pigmentation in Drosera Whittakeri seems to be confined to 
2 C. r., 141, p. 838. 
